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Tippmann Pneumatics

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Tippmann Model 98 Custom
with Response Trigger
by Bill Mills
December 2000

The Tippmann Model 98 has earned a solid reputation.  By combining the durability and reliability of their previous designs with a light trigger pull, and a design that reduces manufacturing costs, Tippmann Pneumatics delivered a winner in the Model 98.

So why a design update?  While the Model 98 has been successful in its original design, many M98 owners have chosen to take their paintguns to airsmiths, or do work or instal parts themselves to tweak their paintgun to their own taste.  While the new 98 Custom does not add these custom features to the stock design, it is better prepared to accept upgrades down the road.

At a glance, the first difference visible in the two paintguns is the lettering on the left side of the receiver.  The new text reads "TIPPMANN 98 CUSTOM" rather than "TIPPMANN MODEL 98."  The text is also located further forward on the receiver.  This is due to the removal of the shark gill ridges that were a part of the original 98. 

Moving to the top of the receiver, there is a new ridge running down either side.  The M98 sight rail is a Weaver style, while many sights for paintball and airguns are built to mount on a 3/8" rail.  The 98 Custom features a dual rail, which can accept 3/8" mount sights and most Weaver mount sights (some Weaver mount sights have a tight clearance which prohibits mounting on a dual standard rail).

The fore grip/vertical ASA section of both receivers is the same, but moving further back, the 98 Custom sports a new trigger and trigger guard.  Two finger triggers are a popular after market upgrade.  Unfortunately, they don't fit in the M98's single trigger guard.  Upgrading meant cutting the old guard from the two receiver halves, and then installing some sort of after market guard, which often meant more cutting or milling on the receiver halves.  The 98 custom trigger guard is a separate piece, making the change to a 2 finger trigger and matching guard a drop-in component upgrade.

The back edge of the 98 Custom trigger features a flat edged protrusion, that is used by the Response Trigger, if installed.

Also new on the 98 Custom are the grips.  While their style wraps around the grip frame, they are curved with a tighter radius, changing their overall shape.  Also, they are two pieces which mate together in the front, rather than being a single wraparound piece.  The left grip has an access hole which exposes the receiver screw at the bottom rear of the grip.  This allows the receiver to be opened for maintenance or repair without needing the extra step of removing the grips.

Mounted below the grip is the bottom line ASA adapter - another area of change in the 98 Custom.  Rather than feeding gas out the right hand side and into an elbow to a hose, the new adapter is threaded in its front.  This centered placement gets rid of the edges and corners of the elbow sticking out on the right hand side.

Internally, more changes are to be found.  Along the lower edge of the receiver are two divots.  They provide alignment, and a thin metal wall to be drilled out to install the gas lines needed for the Response Trigger upgrade.  In addition, inside the grip area, there is a cylindrical indentation to allow space for the Response Trigger ram.  There are also thin sections on either side, thin enough to be punched out like the slug on an electrical box.  These panel areas are to allow for future upgrade with the planned electronic trigger kit.

The Response Trigger

One of the first upgrades designed just for the 98 Custom is the Response trigger.  Much like the Reactive Trigger feature of an Automag RT, the Response Trigger "kicks back" with more force once the paintgun fires.  The result is that the user is able to fire more rapidly, because the added trigger return force means less time is spent releasing the trigger for the next shot.

The Response Trigger achieves this by channeling a portion of the CVX valve's blowback gas through a short section of tubing on the right hand side of the receiver.  There is no effect on gas efficiency, as the gas used to drive the response cylinder is routed out of the receiver from the airspace between the hammer (rear bolt in Tippmann's terminology) and valve.  If the gas were not routed to the cylinder, it would instead escape to the outside air when the hammer reaches the rear of its stroke.

When the Response cylinder receives a burst of gas through the ducting system, it extends, pushing the trigger forward rapidly.

Just how responsive/reactive should a trigger be?

Within the NPPL, and many other leagues, reactive triggers are allowed, so long as they are not too reactive.  The exact lines of what is and is not allowed are somewhat fuzzy, but according to NPPL Rules Committee Chairman, reactive triggers become unacceptable when they are "runaway triggers."  As a trigger is tuned to become more reactive, there comes a point where the trigger return weight is so much greater than the trigger pull weight that a light pressure fires a string of shots without the user intentionally making distinct pulling motions, even through a complete trigger cycle occurs for each shot.  Rules aside, a real problem with runaway triggers is the possibility of firing faster than current  loader technology can deliver paintballs to the paintgun. 

With the Tippmann Response Trigger, this is not a problem. A small 90 degree Clippard valve mounted at the point where the gas hose enters the receiver allows the burst of gas to the cylinder to be limited from completely off, to fully reactive.  A lock nut allows the setting to be locked in place if field or tournament rules disallow reactive triggers, or limit how reactive they may be.  Placement of the valve is fine for players who use their index finger, but players that prefer to shoot with their middle finger may find the external valve getting in the way unless they switch to a two finger trigger. 

Performance - This is where it gets fun...

"It rips!" is a pretty good summary.  In testing the 98 Custom with Response Trigger for review, it became apparent that if dialed wide open to a runaway trigger, it is possible to outpace a Revolution loader and chop paint.  Setting the trigger to a good level of reactivity makes quick firing very practical.

To see the difference the Reactive Trigger can make, a test set-up was used with a barrel plug equpped with an impact transducer wired to a computer waveform recorder.  The result is a nice chart showing each time a burst of gas is fired into the barrel.  Below are two charts, one a string fired "as fast as possible" with the Response valve closed.  The second, is recorded with a runaway trigger cycling with the valve completely open.  Click on the graphs for a more detailed view.

Rapid Firing with Response Trigger Off

Bursts fired with Response Trigger on 100%

The data clearly shows the power of the Response Trigger.  It is important to keep in mind that this data does not represent a perfect empirical test - is it is subject to variances in the person pulling the trigger.  It is also important to note, that the testing denotes bursts of gas, and not loading/firing, or the ability of the valve to charge at high rates of fire without velocity drop-off (i.e. - it would be a misinterpretation to say "the test proves that Tippmann's shoot fine at 20 shots/second"). 

With the Response trigger fully active, the cyclic rate in a runaway trigger burst is roughly double what the test shooter could achieve without it.  Light pulls on the trigger often resulted in 2 or three round bursts.  Just a minute or so of dry firing while adjusting the Response Trigger valve is all that is needed to prevent a runaway trigger.  When tuned to the shooter's taste, the 98 Custom enters a new realm of firepower, without feed problems.

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